<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    var o = {
        a:'aa'
    }
    o.b = 'bb';

    Object.defineProperty(o,'c',{
        configurable:true,
        value:'ccc',
        enumerable:true,            //for in 中看不到这个属性，但是能够读取的 Object.keys JSON.stringify
        writable:true
    })

    console.log(o.c);
    o.c = 'frank';
    console.log(o.c);
    for(var i in o){
        console.log(i);
    }
//    var s = JSON.stringify(o);
    Object.defineProperty(o,'c',{
        value:'ccc',
        enumerable:false            //for in 中看不到这个属性，但是能够读取的 Object.keys JSON.stringify

    })
    o.c = 'tom';
</script>
</body>
</html>